The present invention relates to a process for imparting a water resistance to molded polysaccharide.
According to aggravation of an environmental pollution by waste, plastic (a polymer compound and its combination substance) which is degradable to low molecular weight compounds by microorganisms in the natural world is called a biodegradable plastic and has been noted.
Since a natural polysaccharide such as starch is excellent as a raw material for a biodegradable plastic in stability, steady supply, low cost and the like, its utilization has been examined. However, there remains several problems in order to enlarge its application, and as one of them is cited the point that a lot of natural polysaccharides having poor water resistance due to their high hydrophilicity.
If these defects can be overcome with a low cost, the function and value of a natural polysaccharide as a biodegradable plastic can be improved remarkably.
Further, a technology to change the property of polysaccharide by bonding the amino group of amino acid or protein to polysaccharide having the carboxyl group is known.
1:
JP, T, H3-502704 (U.S. Pat. No. 4,937,270)
A water insoluble biocompatible gel is prepared by the introduction of an aminoester to hyaluronic acid by forming an amide bond with carbodiimide as a catalyst.
2:
JP, A, H8-23975 (EP, A, 710,666)
A polymer carbodiimide compound is carried on a surface of a base material (including a natural polymer like polysaccharide) and fixed with a biologically active substance (including protein with a physiological activity).
3:
Bioconjugate Chem., 2, 232-241 (1991)
A reaction mechanism and a product in case of modifying hyaluronic acid chemically with a primary amino acid using carbodiimide are reported.
4:
Biosci. Biotech. Biochem., 58, 174-177 (1994)
Biosci. Biotech. Biochem., 59, 2203-2206 (1995)
J. Agric. Food Chem., 43, 2007-2011 (1995)
Physicochemical properties and enzyme reactivities of bonded products in a combination such as lysozyme and carboxymethyl dextran, amino acid and carboxymethyl starch, or milk protein and carboxymethyl starch, by the use of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as the carbodiimide are reported. In the report, it is reported that the bonded products obtained decrease in a water absorption property and the solubility in water.
On the other hand, it is also considered that a carboxyl group of amino acid or protein is bound with polysaccharide having an amino group.
However, in the prior art a technology for imparting water resistance as to a molding consisting of polysaccharide by chemically bonding amino acid, peptide or protein to its surface has not been known at all.
Further, prolamin is protein mainly contained in grain, and has a unique property as protein that it is insoluble in water and a salt solution and soluble in alcohol containing water and acetone containing water. As prolamin are known, for example, gliadin in wheat, hordein in barley, zein in corn, and the like. In particular as to zein, it is known that a coated membrane which is excellent in properties such a water-resistance, acid-resistance, thermal resistance, electrical insultion, antioxidizing, digestive enzyme-resistance (enteric solubility), deodorant, adhesion, and biodegradation properties is formed when coating a zein solution in an alcohol of 1-4 carbon atoms or acetone on surface of an object for treating material by means such as spraying, coating, or dipping.
By utilizing these properties are considered technologies on a prolamin membrane by various zeins in a food field (JP, A, S53-38646, JP, A, S58-193646 (EP, A, 90559), JP, A, S60-248158, JP, A, H4-297414 (U.S. Pat. No. 5,077,053), JP, A, H5-23117, JP, A, H4-28768, JP, A, H6-303902, JP, A, H6-284875, JP, A, H7-32610, JP, A, H7-327634, JP, A, H7-231756 (U.S. Pat. Nos. 5,643,667 and 5,733,638) and the other fields such as a medicinal field (JP, A, S53-26318 (U.S. Pat. No. 4,137,300), JP, A, S59-220175, JP, A, S60-221078 (U.S. Pat. No. 4,888,171), JP, A, S61-141862, JP, A, S63-101319, JP, A, H3-65145 (U.S. Pat. No. 5,098,718), JP, A, H4-364123, JP, A, H4-334317, JP, A, H5-186335, JP, A, H5-186337, JP, A, H5-221859, JP, A, H6-24963, JP, A, H6-133735, JP, A, H7-252140 (U.S. Pat. No. 5,500,227).
However, in the past, a technology for imparting water resistance to said molding by chemically bonding prolamin such as zein to surface of a molded polysaccharide was not known at all.
Nevertheless, owing to the point that a lot of natural polysaccharides having poor water resistance due to their high hydrophilicity, there has been restriction of their utilization.
The invention has the aim for imparting water resistance to a molded polysaccharide which having poor water resistance due to its high hydrophilicity.
As a result of extensive studies to solve the above problems, the inventors found that bonding chemically prolamin such as zein to a surface of a molded polysaccharide which having poor water resistance due to its high hydrophilicity can impart water resistance, further continued the studies, and have thus accomplished the invention.
Namely, the invention is as follows.
1. A process for imparting water resistance to a molded polysaccharide by bonding a prolamin to a surface of the molded polysaccharide.
2. A process for imparting water resistance to a molded polysaccharide according to claim 1, wherein the polysaccharide contains a functional group with a prolamin bonding property.
3. A process for imparting water resistance to a molded polysaccharide according to claim 2, wherein the functional group with a prolamin bonding property is a carboxyl group.
4. A process for imparting water resistance to a molded polysaccharide according to claim 2, wherein the functional group with a prolamin bonding property is an amino group.
5. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3 or 4, wherein the polysaccharide is starch.
6. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3, 4 or 5, wherein the bonding of prolamin is carried out in the presence of carbodiimide.
7. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3, 4, 5 or 6, wherein the bonding of prolamin is carried out in an alcohol of 1-4 carbon atoms or acetone solutions of prolamin.
8. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3, 4, 5, 6 or 7, wherein prolamin is zein.
9. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein the alcohol or acetone contains water.
10. A process for imparting water resistance to a molded polysaccharide according to claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the alcohol is ethanol.
As described above, imparting water resistance by prolamin such as zein was generally made in the past by coating with prolamin such as zein.
On the contrary, in the invention prolamin such as zein is bound to a surface of a molding of polysaccharide having a functional group with a bonding property for prolamin such as zein, in particular a carboxyl group or an amino group, thereby improving the water resistance of said molding.
The bonding amount of prolamin such as zein is about 0.6%, an extremely minute amount. In the invention, regardless of such an extremely minute bonding amount of prolamin such as zein, it was totally an unexpected result that the water resistance could be given to the molded polysaccharide.
As described below, as to a swelling property of a molded polysaccharide by contact with water, a carboxymethyl starch membrane (CMS) or the same membrane but to which zein are allowed to simply contact with starch (hereinafter referred to as xe2x80x9cmixed membrane (CMS+Zein)xe2x80x9d), swells remarkably, whereas an inventive carboxymethyl starch membrane, to which zein is allowed to chemically bond (hereinafter referred to as xe2x80x9cbonded membrane (CMSxe2x88x92Zein)xe2x80x9d), swells hardly.
Thus, the fact that CMS membrane and the mixed membrane (CMS+Zein) swell remarkably is considered to be due to a water absorption of starch in said membranes.
On the contrary, in the bonded membrane (CMSxe2x88x92Zein) such swelling is inhibited, and this is considered to be due to the fact that the starch membrane is coated with zein, by the bonding of zein, resulting in the difficulty of a contact between starch and water molecules.
Therefore, it is considered that the unexpected effect of the invention is brought about by a synergistic effect of a chemical aspect in which a stable and tight bonding is formed by a chemical bonding between a functional group with a bonding property for prolamin such as zein in polysaccharide consisting of a surface of a molding, in particular a carboxyl group, and prolamin such as zein, and a physical aspect in which the surface of said molding is coated with bound prolamin molecules such as zein having a water resistance.
Thus, as is evident from the above unexpected effect of the invention it is understandable that there is a special significance in the treatment of prolamin such as zein in the invention.